1. Field of the Invention
The invention relates to a projection system capable of automatic focus adjustment. In particular, the invention relates to a projection system that automatically adjusts the projection focus by an evaluation function applied in projective image analysis.
2. Description of the Related Art
Traditionally, projection systems have relied on the user""s visual assessment to adjust the focus of the projected image.
FIG. 1 shows a schematic diagram of the automatic focal adjustment device of a typical LCD projection system. In a Japan Patent Laying Open Hei No. 11-119185, as shown in FIG. 1, three LCD display devices 1400r, 1400g and 1400b respectively produce red, green and blue images through a cross prism 4000 to form a color image. The color image passes through a semitransparent reflective device 3000 to form images on the screen s through a projective lens 1000. The image on the screen s is reflected on an optical receiving device 500 through the semitransparent reflective device 3000. Further, a signal generation device 1600, a control device 9000, an operation device 8000 and a focus adjustment/control device 6000 are used to analyze and compare each image on the focal position of the projective lens 1000. However, as such, a semitransparent reflective device is required, which increases the distance from the projective lens 1000 to the three LCD display devices. As a result, the rear focal length of a projective lens and design difficulty for the projective lens are increased concurrently.
Accordingly, an object of the invention is to provide a projection system that automatically adjusts the focus of an optical projection device by an evaluation function applied in projective image analysis. The projective system includes a total reflection element, an image reader, an analysis system and a server device. The image reader reads the projective image guided by the optical projection device and the total reflection element and outputs a read signal. The analysis system analyzes the read image by an evaluation function and determines the clearest image on the projective plane so as to output an adjustment signal. The server device automatically performs the focal adjustment to the optical projection device based on the adjustment signal.
The invention has the advantage that the projective system can automatically adjust the focus of the optical projection device in any projective distance to produce the clearest image.
The invention is characterized in that the analysis system uses a modulation transfer function (MTF) analysis to have the clearest projective image.